This invention relates to a method for producing a magneto-optical recording medium which, like a magneto-optical disk allowing overwriting through light intensity modulation, has a laminated structure composed of a plurality of magnetic layers made of alloys of rare earth metals-transition metals.
Recently, in the field of magneto-optical recording, demands for higher functions such as high rate of data transmission and high density of recorded data are increasingly growing. To meet such demands, various techniques have been put into practice. For example, a representative technique enabling such high rate of data transmission includes overwriting through light intensity modulation, and another technique enabling such high density of data recording includes magnetically induced recording with super resolution (MSR).
These techniques can be put into effect when a laminated magnetic film is realized, instead of a conventional magneto-optical disk composed of a single magnetic layer, which includes a plurality of magnetic layers made of alloys of rare earth metals-transition metals alternately place one over another.
Such laminated magnetic film is usually produced with a sputtering apparatus which contains a plurality of shooters in a single filming chamber. During operation, materials different in composite elements are charged into individual shooters, and a substrate is placed opposite to those shooters one after another. Particles shot from individual shooters are deposited one over another on the substrate, to form a magnetic disk with a laminated structure having a plurality of layers of different compositions.
For a laminated film to be made by sputtering as described above, conventionally, a plurality of substrates are mounted onto a circular plate, and the plate is rotated such that the substrates mounted thereupon are placed opposite to the shooters one after another, and that all the substrates develop films on their surface at the same time. The composition of a given magnetic layer is adjusted after the shutter placed in front of a shooter has been opened or closed, or after driving powers delivered to the shooter have been adjusted appropriately.
As described above, techniques such as direct overwriting through light intensity modulation or magnetically induced recording with super resolution can be put into effect only after they are applied to a laminated magnetic film with a plurality of layers made of alloys of rare earth metals-transition metals, and different in composition from one another. However, even if a magneto-optical recording medium with such laminated magnetic layers is actually produced, it will not always give the properties as have been theoretically expected stably.
To put it more specifically, even if a magneto-optical recording medium with such laminated structure is actually produced, the properties necessary for the expected high performance will be often present unevenly on the interfaces of laminated structure. Or, if a large number of magneto-optical recording media are produced, the properties in question of individual media will show a wide variation. These problems form the reason why conventional magneto-optical recording media with a laminated structure whose properties are sufficiently good to allow high grade recording have never been stably produced.